The present invention relates to tubular fluid flow devices having a varied outer dimension and which are used in high pressure, rapidly cycling temperature environments, and more particularly to such devices employed in severe service metal-seated isolation ball valves, ball valve isolation methods, catalyst transfer, for example, to or from a reactor such as an ebullated bed reactor, and the like.
In some severe service environments, line isolation valves are subjected to frequent and extreme temperature and pressure cycles as the valve is opened and closed. Because the valve components have different dimensions, for example where end connectors such as flanges are employed, heat transfer may not be uniform and stresses can develop within the materials of construction, which may lead to premature thermal fatigue stress cracking.
In the transfer of catalyst from a reactor, for example, the isolation valves in the transfer line which are initially at ambient temperature may be fully opened to receive the flow of catalyst fines at temperatures over 400° C., rapidly heating the valve components. When the transfer is completed, the isolation valve is closed and cools to ambient temperature before another transfer cycle is initiated. The thermal/pressure cycle may be repeated more than once a day. Because components in thermal contact with the hot fluid flow can be asymmetrical and/or have different dimensions such that heat transfer occurs at different rates to produce temperature differences in the materials, isolation valves used in this service can suffer from premature thermal fatigue stress cracking, and can also be subject to erosion due to the abrasive nature of the catalyst particles.